Interpretive Summary: It has been suggested that patients with nonalcoholic steatohepatitis (NASH), or with inflamed livers, have a high risk for liver cancer. However, it is unknown whether an inflamed liver caused by a high fat diet causes liver cancer. In the present study, rats were injected with a low dose of a liver carcinogen and then fed either a control diet or a high fat diet for 6 weeks. Results showed that rats fed a high fat diet developed a significantly higher rate and number of lesions in the liver along with greater fat accumulation and inflammation of liver cells. These data clearly demonstrates that liver cancer can be promoted by high-fat diet-induced liver inflammation.

Technical Abstract:
It has been suggested that patients with nonalcoholic steatohepatitis (NASH) are at a high risk for liver cancer. However, it is unknown whether high-fat diet induced NASH promotes hepatocarcinogenesis. In the present study, Sprague-Dawley rats were injected with a low dose of hepatic carcinogen diethylnitrosamine (DEN), and then fed either a Lieber-DeCarli control diet (CD) or a high-fat diet (HFD) for 6 weeks. Liver histology and the hepatic placental form of glutathione S-transferase (P-GST) positive foci were examined. Expression levels of proliferating cell nuclear antigen (PCNA), cyclinD1, a phosphorylated MAPK (including extracellular signal-regulated kinase (ERK)) and p38, as well as TNF-alpha and NF-kappaB, were measured in the liver. Induction of lipid peroxidation end products (malondialdehyde plus 4-hydroxynonenal) in liver and apoptotic hepatocytes were also assessed. Results showed that HFD-fed rats developed significantly higher incidence and multiplicity of P-GST positive foci along with more fat accumulation, infiltration of inflammatory cells, and higher lipid peroxidation in the liver, as compared to rats fed the CD. The high prevalence of hepatic lesions in the liver was accompanied by greater PCNA expression and cyclinD1 protein concentration, but little change in hepatocyte apoptosis. HFD feeding elevated hepatic phosphorylated ERK but reduced phosphorylated p38 as compared with CD feeding. In addition, a significantly higher expression of TNF-alpha mRNA and nuclear NF-kappaB p65 proteins were observed in HFD group than those in CD group. These data clearly demonstrates that NASH induced by a high-fat diet promoted DEN-initiated early hepatocarcinogenesis, which was associated with elevated TNF-alpha/NF-kappaB signaling and MAPK related hepatocyte proliferation.